TUESDAY, July 16 (HealthDay News) -- High humidity and temperatures in the 90s could test the endurance of millions of Americans in the eastern and central parts of the country for days to come, experts warn.

The U.S. National Weather Service said thermometers will stay in the 90s for the next few days in the Northeast, Mid-Atlantic and Midwest. However, the service's heat indices -- which factor in humidity to calculate how hot the weather feels -- will push past 100 degrees, CNN reported.

The sticky heat is expected to extend westward as the week proceeds, covering much of the central and eastern United States.

Health experts said there are key steps everyone can take to minimize their risk from extreme heat.

One essential step: Check up on elderly or ill relatives living on their own.

"Due to various reasons, the elderly are prone to suffer from the extreme heat," said Dr. Salvatore Pardo, associate chairman of the emergency department at Long Island Jewish Medical Center in New Hyde Park, N.Y.

"It is vital for loved ones and friendly neighbors to enter the home and make sure they have functioning air conditioning or access to a cool environment -- for example, a cooling center, senior center, public shopping mall -- during extreme heat events," he said. "This should be done at the beginning, during and after the extreme heat event."

Keeping the shades drawn in the daytime can keep homes cooler, he said, and "if you live in a split-level home, stay downstairs. Heat rises, so upstairs will always be hotter than your living room. Open windows upstairs if you have no air conditioning to keep the room cool, and have a fan blowing."

Alcoholic beverages dehydrate, so stick to water or beverages without alcohol, sugar or caffeine, Ammazzalorso said. Wear light, light-colored and loose clothing to stay cooler.

"Let the children play outside in the early morning or early evening when the air quality is at a healthier level and the temperatures are cooler," he added. "Head to a local swimming pool or beach to cool off, but never swim alone and be sure to observe all posted swimming advisories."

According to Ammazzalorso, signs of heat exhaustion include skin that is cool, moist and pale but may look flushed at times. Dizziness or fainting, nausea or vomiting, fatigue and headaches are also potential signs of heat exhaustion.

Signs of an even more serious condition known as heat stroke include red, hot and dry skin, high body temperatures (105 degrees or above), a rapid and weak pulse, rapid and shallow breathing and changes in consciousness. In these cases, 911 should be dialed immediately, Ammazzalorso said.

Extra precautions also need to be taken to keep your pets safe in the heat. The Humane Society of the United States recommends the following:

Never leave your pets in a parked car, not even for a minute and not even if the car is running and the air conditioning is working. If you see an animal in distress in a parked car, call the nearest animal shelter or police.